Journal of Geosciences, 66 (2021), 37–50

DOI: 10.3190/jgeosci.318

Original paper

Krupičkaite, Cu6[AsO3(OH)]6·8H2O, a new copper arsenate mineralfrom Jáchymov (Czech Republic)
Gwladys STECIUK*1, Jiří SEJKORA2, Jiří ČEJKA2, Jakub PLÁŠIL1, Jan HLOUŠEK3,†
Institute of Physics, Academy of Sciences of the Czech Republic v.v.i, Na Slovance 2, 182 21 Prague 8, Czech Republic;
steciuk@fzu.cz
2
Department of Mineralogy and Petrology, National Museum, Cirkusová 1740, 193 00 Prague 9, Czech Republic
3
Jáchymov, Czech Republic;†
deceased*
Corresponding author
1

Krupičkaite, ideally Cu6[AsO3(OH)]6·8H2O, is a new supergene mineral from the Rovnost I shaft in Jáchymov, Czech
Republic. It forms aggregates of pale greenish-blue color and grows along with supergene minerals crystallizing on
the strongly altered relics of massive tennantite, Bi-rich tennantite, galena, chalcopyrite, bornite, and chalcocite with
disseminated uraninite in quartz. For a long time, krupičkaite has been left out due to its quite inconspicuous ap­pearance
that can be mistakenly referred to as geminite. At the ambient temperature, krupičkaite is monoclinic, a = 15.504(7)Å, b = 18.144(7) Å, c = 10.563(5) Å, β = 103.30(4)°, V = 2891.5(2) Å3, Z = 4, space group P21/m. Its structure has
been solved and refined from 3D electron diffraction and further studied by Raman spectroscopy. The layered structureis built upon the alternation of two different copper-arsenate sheets stacked along b presenting a characteristic wave
shape along the a–axis and separated by a thick interlayer with channels containing only H2O. The collapsed chains ofcopper polyhedra are connected the same way as in geminite through AsO4 tetrahedra. Krupičkaite joins the family ofcopper arsenate minerals with which it shares structural similarities at the level of the As-Cu layers with the lindackerite
supergroup, slavkovite, or yvonite.
Keywords: krupičkaite, copper arsenate, crystal structure, electron diffraction, acid-mine-drainage, supergene weathering
Received: 4 November 2020; accepted: 10 March 2021; handling editor: F. Laufek
The online version of this article (doi: 10.3190/jgeosci.318) contains supplementary electronic material.

1. Introduction
Under oxidizing conditions, decomposition of hypogene/primary As-containing sulfides and sulfosalts potentiallyleads to a release into the environment of significant
amounts of arsenic, heavy metals and metalloids. In ore
deposits, supergene minerals are formed as resulting
products of these reactions and they serve as a temporary
or final sink for such toxic ele­ments otherwise released
into the groundwater systems. The danger associated witharsenic in the environment, combined with its unusually
great mineralogical diversity poses a set of specific challenges to mineralogy and environmental geochemistry(Majzlan et al. 2014; Christy 2015). To give properanswers and solutions to the environmental problems,
the detailed knowledge of mineralogy, crystallography,
physical and chemical properties of As-containing oxysalts are of great importance as it can be used to assess
and predict the behavior and the mobility of elements
during weathering, both natural or anthropogenicallyinduced (e.g., Borčinová Rad­ková et al. 2017; Keim etal. 2018; Majzlan et al. 2018, 2021; Đorđević et al. 2019,and references therein).

Krupičkaite, ideally Cu6[AsO3(OH)]6·8H2O, is a newcopper arsenate hydrate found from the strongly weathered material originating from the famous Rovnost I shaftin Jáchymov, Czech Republic. It has been formed via oxidative weathering of a complex hypogene mineral association (including namely tennantite and Bi-rich tennantite)at the Geister vein. Although it is currently known only
from a few specimens, it is likely to be much more common and overlooked due to its relatively inconspicuous
ap­pearance that can be mistakenly referred to as geminite.
The new mineral honors the name of professor Jiří“George” Krupička (born in Prague, Czech Republic,
May 5, 1913; died in Edmonton, Canada, April 24, 2014),
first of all, a polymath; linguist, geologist and astronomer
by education.
The new mineral was approved by the CNMNC IMA
under the code IMA 2020–032. The holotype specimen of
krupičkaite is deposited in the collections of the Department of Mineralogy and Petrology, National Museum in
Prague, Cirkusová 1740, 19300 Praha 9, Czech Republic
under the catalogue number P1P 18/2020. The aim of thiswork is to document the physical and chemical attributesof the new species, and to shed light on its crystal structure.
www.jgeosci.org

Gwladys Steciuk, Jiří Sejkora, Jiří Čejka, Jakub Plášil, Jan Hloušek

2. Occurrence
Krupičkaite was found in 1978, in an old ore-stope nearsurface workings at the 3rd Geister level of the Rovnost I(former Werner) mine. Rovnost I mine, in Jáchymov(Czech Republic), opened and remained the main shaftof the so-called Western district of Jáchymov mines,
situated at the center of the Rovnost ore node. This stope
was reopened during the first half of the 19th century andlater on in the 1950ties. The main aim was mining for
Ra and U, used for glass-staining in the 19th century andlater implementing the Soviet atomic arsenal. The moredetailed information about history, geology and mineralogy of this particular locality can be found elsewhere(Ondruš et al. 2003; Hloušek et al. 2014; Horák et al.
2014; Plášil et al. 2017; Škácha et al. 2019). The mineralrichness of the locality results from the occurrence ofboth the recently/sub-recently formed minerals connectedwith the post-mining processes, and the supergene minerals formed in-situ in the oxidation zone (associationof uranyl arsenates and vanadates; association of Pb-Cu
supergene minerals and minerals containing Y and REE).
The shaft where krupičkaite was found is informallycalled the “lindackerite stope” by mineral collectors. This
name is due to frequent occurrences of the lindackeritesupergroup minerals: lindackerite, veselovskýite (Sejkora
et al. 2010a), hloušekite (Plášil et al. 2014a), pradetite(unpublished data of the authors) and klajite (Plášil etal. 2014b; Hloušek et al. 2014). A copper-dominantvivianite-group mineral, babánekite (Plášil et al. 2017),
has been found from the same material as krupičkaite.
Supergene minerals crystallize on the strongly alteredrelics of massive tennantite, Bi-rich tennantite, galena,chalcopyrite, bornite, and chalcocite with disseminateduraninite in quartz (in the absence of carbonates).
Krupičkaite grows along with those above-mentioned
minerals, forming rather inconspicuous aggregates ofpale greenish-blue color. The richest specimens were

found in the intensively cemented fragments with relicsof primary minerals.

3. Appearance and physical properties
Krupičkaite appears in rounded or grape-like aggregatescomposed of hundreds of microcrystals that are not larger
than the first microns. These aggregates have greenishblue color, occasionally with a grey tint, and reach up to
4 mm in size, sitting at the surface of the supergene crusts(Fig. 1). Krupičkaite has a vitreous luster. The streak iswhite. The Mohs hardness is estimated at 2 (based on
scratch tests). No cleavage nor tenacity has been observed.
The mineral is not fluorescent under long- or short-wave
ultraviolet radiation. A density of 3.123 g/cm3 was calculated using the empirical formula and unit-cell parameters
obtained from powder X-ray diffraction. Direct density
measurements were not undertaken due to the paucityof pure material. Optical properties could not have been
determined due to the extremely small size of the crystals;
the mean n calculated from Gladstone–Dale rule is 1.597(empirical formula) or 1.5975 (ideal formula).

4. Chemical composition

Chemical analyses of krupičkaite were carried out with a
Cameca SX 100 electron microprobe (WDS mode, 15 kV,
5 nA, 20 μm defocused beam diameter). Analytical lines
and standards are given in Tab. 1; peak counting times
were 10–20 s and the counting time for the backgroundtheir half. The measured intensities were processed
for matrix effects using the “PAP” correction routine(Pouchou and Pichoir 1985). Water could not be analyzed
directly because of the small amount of pure material
available and was calculated on the basis of 8 H2O fromthe structure analysis. Results (average of 22 analyses)
are given in Tab. 1. After the
Tab. 1 Analytical data (wt. %) for krupičkaite
inclusion of water content, thehigher analytical total indicatesConstituent
Mean
Range
Standard deviation
Probe Standard
partial dehydration of the samCuO
31.83
29.35–33.12
0.95
chalcopyrite
ple under vacuum in the EPMA
CaO
0.22
0.08–0.50
0.11
fluorapatitechamber.
CoO
1.95
1.62–2.58
0.25
CoThe empirical formula of theNiO
1.90
1.45–2.71
0.34
Niaggregate of krupičkaite, on the
MnO
0.05
0–0.230.06
rhodonitebasis of 32 anions apfu, is (Cu5.16
ZnO
0.68
0.43–0.87
0.11
ZnO
C o 0 . 3 4 N i 0 . 3 3 Z n 0 . 11 C a 0 . 0 5 F e 0 . 0 1
FeO
0.06
0–0.170.05
hematite
SiO2
0.14
0–0.440.13
sanidine
Mn0.01)Σ6.01(AsO3OH)5.97(SiO4)0.03
As2O5
53.16
50.86–54.75
1.04
clinoclase(PO 3 OH) 0.01 ·8H 2 O. The ideal
P 2O 50.06
0–0.31
0.09
fluorapatite
formula Cu6[AsO3(OH)]6·8H2O
H2O*
15.35
requires CuO 34.97, As 2 O 5
Total
105.4050.51, H2O 14.52, total 100.00* Content of H2O was calculated on the basis of ideal composition derived from results of the crystal wt. %. Kupičkaite is visibly
structure study

38

Krupičkaite, a new copper arsenate from Jáchymov

Fig. 1 a) Krupičkaite aggregates on gangue used for the crystallographic analysis. b) Two krupičkaite crystals selected for 3D ED data acquisition collected on the sample shown in a). c) Light greenish–blue hemispherical aggregates of krupičkaite on strongly supergene altered gangue,
Jáchymov; holotype specimen, width of the photograph is 3.7 mm, photo J. Sejkora.

insoluble in H2O and soluble in dilute (10 %) HCl, atroom temperature.

5. Raman spectroscopy
The Raman spectrum (Fig. 2) was collected in therange 4000–50 cm –1 using a DXR dispersive Raman
Spectrometer (Thermo Scientific) mounted on a confocal Olympus microscope. The Raman signal was
excited by an unpolarised red 633 nm He-Ne gas laserand detected by a CCD detector. The experimental
parameters were: 100× objective, 10 s exposure time,
100 exposures, 400 lines/mm grating, 50 μm pinhole
spectrograph aperture and 5 mW laser power level. The
instrument was set up by a software-controlled calibration procedure using multiple neon emission lines(wavelength calibration), multiple polystyrene Raman
bands (laser frequency calibration) and standardized
white-light sources (intensity calibration). Spectral
manipulations were performed using the Omnic 9 software (Thermo Scientific). The main bands observed

39

4000

3000

144
96

330

417
372

1615

2386

2914

3133

3422

495

455

756

209

812

Raman intensity (arbitrary units)

824

847

Gwladys Steciuk, Jiří Sejkora, Jiří Čejka, Jakub Plášil, Jan Hloušek

2000

1500
Raman shift (cm–1)

1000

500

Fig. 2 Raman spectrum of krupičkaite from Jáchymov (split at 2000 cm –1).

are (in wavenumbers): 3422, 3133, 2914, 2386, 1615,
847, 824, 812, 756, 495, 455, 417, 399, 372, 330, 209,
144 and 96 cm –1. Very weak broad Raman bands with
topics at 3422 and 3133 cm –1 are assigned to the ν OH
stretching vibrations of structurally distinct differently
hydrogen-bonded water molecules. Very weak broad
Raman bands with topics at 2914 and 2386 cm–1 areconnected with ν OH stretching vibrations in hydrogenbonded (AsO 3OH)2– units. A very weak broad Raman
band at 1615 is assigned to the ν 2 (δ) H 2O bending
vibrations of water molecules. The most prominent
very strong Raman bands at 847 and 756 cm –1 withshoulders at 824 and 812 cm –1 are attributed to overlapping ν 1 (AsO 3OH) 2– symmetric stretching, and ν 3(AsO3OH)2– antisymmetric stretching vibrations. Raman
bands 495, 455, 417 and 399 cm –1 are connected withthe ν4 (HOAsO3)2– bending vibrations. Raman bands at
372 and 330 cm –1 are related to the ν 2 (δ) (HOAsO3)2–
bending vibrations. Raman band at 209 cm–1 is assigned
to the ν (OH⋅⋅⋅O) stretching vibrations and those at 144
and 96 cm–1 to lattice modes (Vansant et al. 1973; Čejka
et al. 2011; Sejkora et al. 2010b, 2020).

40

6. Crystallography

6.1. Powder X–ray diffraction
X–ray powder diffraction data of krupičkaite (Tab. 2)
were recorded at room temperature using a Bruker D8Advance diffractometer equipped with a solid-state LynxEye detector and secondary monochromator producing
CuKα radiation housed at the Department of Mineralogy
and Petrology, National Museum, Prague, Czech Republic. The instrument was operating at 40 kV and 40 mA.
To minimize the background, the powder samples wereplaced on the surface of a flat silicon wafer. The powder
pattern was collected in the Bragg–Brentano geometry in
the range 3–70° 2θ, step 0.01° and counting time of 20s per step (total duration of the experiment was ca. 30
hours). The positions and intensities of diffractions were
found and refined using the Pearson VII shape function of
the ZDS program package (Ondruš 1993). The unit-cellparameters were refined (starting from those obtainedby the electron diffraction) by the least-squares programof Burnham (1962) as follows: a = 15.504(7) Å, b =Krupičkaite, a new copper arsenate from Jáchymov

18.144(7) Å, c = 10.563(5) Å, β= 103.30(4)° and V = 2891.5(2)Å 3.

6.2. Electron diffraction

Tab. 2 Powder diffraction data (d in Å) for krupičkaite
Iobs.

0.13
100.00
0.03
0.22
0.07
0.07
0.07
0.48
0.13
0.51
0.30
0.13
0.06
1.03

dobs.

11.62219.08955.48094.80964.74404.54574.53414.39454.00703.90943.84483.73443.6871
3.5334dcalc.

11.60079.07195.48394.81484.75854.54244.53604.39853.99593.90953.85083.73353.69293.53483.3683

h

k

1
0
2
3
1
1
0
3
3
1
3
3
4
4
3

1 0
2 0
2 –1
1 –1
3 1
2 –2
4 0
2 0
1 –2
4 1
3 –1
2 –2
1 0
2 –1
4 0

l

Iobs.

0.23
0.16
0.03
0.23
0.11
0.18
0.03
0.07
0.15
0.06
0.17
0.20
0.21
0.19
0.11

dobs.

2.73252.72062.65102.61912.60582.51862.51262.49022.41282.39042.35572.30312.2113
2.1986
2.1573dcalc.

2.73402.72242.65072.61512.60632.51942.51262.49132.40742.39572.35452.30062.2143
2.19932.1512

h

k

0
4
2
4
0
1
3
0
6
4
5
3
7
3
7

4 3
1 2
6 1
5 0
6 2
6 2
1 –4
5 3
2 –2
0 –4
5 –1
7 –1
0 –1
7 1
2 –1

l

Due to the nature of the crystals(powdery, indistinct morphology
even under scanning electron microscope), transmission electron
microscopy (TEM) has been chosen to investigate the structuralproperties of krupičkaite. Aggregates of the new mineral were
gently crushed without solventand deposited on an Au-grid with
0.47
3.3687a thin film of holey amorphous
3.36690 1 3
0.07
2.13442.13162 3 4carbon. The grid was plunged
0.25
3.28193.2823
1 2 –30.11
2.04312.04597 3 –2
into liquid nitrogen and then
0.42
3.24413.2407
4 3 –10.01
1.9973
1.99805 4 –4transferred to a FEI Tecnai TEM
0.06
3.18653.1867
1 0 3
0.25
1.98181.98695 5 2
0.32
3.10783.10434 2 1
0.10
1.9537
1.95616 5 1(acceleration voltage of 200 kV,
0.36
3.0852
3.0942
5 0 –10.17
1.81471.81383 9 1
LaB6) using a Gatan cryo-trans0.18
3.02963.02400 6 0
0.22
1.7832
1.7838
4 8 –3fer holder. The cryo-plunging
0.13
2.97812.9846
1 5 –20.02
1.75751.7566
6 3 3
conditions were necessary to
0.93
2.97242.981203
3
0.01
1.75011.75095 7 2
preserve the hydrated nature of
0.54
2.93722.93563
5–1
0.10
1.7452
1.74465 8 1
krupičkaite under the TEM vacu0.26
2.92862.93004 4 –10.09
1.70661.70560 1 6
um. Without this precaution, our
0.17
2.88772.8838
1 6 –10.15
1.6842
1.6856
1 10 2
TEM experiments showed that
0.22
2.83992.83841 5 2
0.09
1.6803
1.6799
6 4 –5krupičkaite undergoes fast dehy0.08
2.78872.7813
1 4 –3dration inducing a drastic change
2.7546
5 3 –10.33
2.7595in the layer configuration. This is2.75364 0 2
also associated with very strong
diffuse features in the data thatthe crystals under the electron beam during the experihamper a reliable structural analysis. The cryo-plunging
ment. The data reduction was performed using the commethod, initially used for organic and biological samples,
puter programs PETS2.0 (Palatinus et al. 2019). Basedwas recently applied to inorganic samples (Mugnaioli
on two merged data sets, krupičkaite is monoclinic, withet al. 2020; Steciuk et al. 2020; Steciuk et al. 2021). To
a = 15.25 Å, b = 17.59 Å, c = 10.27 Å, β = 103.42°, andcollect 3D electron diffraction (3D ED) data on single
V = 2681.6 Å3 (Fig. 3a). No phase transition is observed
crystals (Gemmi and Lanza 2019), the precession electron
between krupičkaite measured from 3D ED at 100K anddiffraction tomography (PEDT) technique was used (Vinat the ambient temperature (PXRD). The reciprocal spacecent and Midgley 1994; Kolb et al. 2007, 2008; Mugnaioli
sections are consistent with the space group P21/n (withet al. 2009). In order to reduce dynamic effects, 3D ED
the condition h+l = 2n on h0l) (Fig. 3b). The experimental
was coupled with precession electron diffraction (PED)
intensity profile (rocking curve) is fitted using several pa(Vincent and Midgley 1994). PEDT data were recorded at
rameters, including the rocking curve width (RC width =100 K on several crystals with the precession device Nano0.003 Å–1) and the apparent mosaicity (mosaicity = 0.15°)
megas Digistar and a side-mounted CCD camera Olympus(for detailed information, check Palatinus et al. 2019).
Veleta with a 14bit dynamic range and an energy-disperThe high value of the apparent mosaicity is mostly due
sive analyzer Octane silicon drift detector (SDD) EDAX.
to stacking faults resulting in elongated reflections along
The precession angle of the beam was kept at 1°. For eachb* (default values in PETS2.0: RC width = 0.001 Å–1 andselected crystal, a series of non–oriented patterns are colapparent mosaicity = 0.05°). For each PEDT data set, twolected sequentially on all the accessible tilt–range of the
hkl-type files are obtained: one for structure solution andgoniometer by step of 1°. For more details about the data
kinematical refinement and another file dedicated to theacquisition, see Palatinus et al. (2015b) or Gemmi et al.
dynamical refinement where each ED frame is considered(2019). Low illumination settings were used to preserve
41

Gwladys Steciuk, Jiří Sejkora, Jiří Čejka, Jakub Plášil, Jan Hloušek

For krupičkaite, the elongatedreflections did not prevent theRefined structural formulaCu6(H2O)6[AsO3(OH)]6(H2O)2.216
structure solution. However, theUnit-cell parameters (PEDT) 100K
accuracy of refinement is affected.
15.25 Åa
If the dynamical refinement isb
17.59 Åthe most accurate for well-crysc10.27 Åtallized crystals and can easily
90°
α=γ
β
103.42°reach R-factors below 8–10 %V
2681.6 Å3(Palatinus et al. 2015b; Steciuk etZ4
al. 2019a), imperfect crystals tend
Density [g·cm–3]
3.3794
to diffract more kinematically. In
Space groupP21/nsuch a case, the question is then to
Temperature
100 K
evaluate if the use of the dynamiTEM
FEI Tecnai 02
cal theory in the refinement brings
Radiation (wavelength)
electrons (0.0251 Å)
further improvement compared to
Resolution range sinθ/λ
0.1–0.7 Å–1
the refinement ignoring them (kiLimiting Miller indices–21≤h≤20, 0≤k≤24, 0≤l≤14
nematical refinement), especiallyNo. of independent reflections (obs/all) – kinematic 1803/7132
when the dynamical refinement
crs1: 0.1345/0.6285 and crs2: 0.1652/0.3142
Rint (obs/all) – kinematic
takes weeks, as it is the case for
Redundancy
4.892
krupičkaite. Several works al–1
Coverage for sinθ/λ = 0.7Å
0.91
ready report similar issues in the
Kinematical refinement with hydrogen
analysis of 3D ED data by going
No. of reflections (obs/all)
1803/7132
from some diffuse phenomenon
0.2157/0.1785
R, wR (obs)reducing the precision of the re201
N parameters
Dynamical refinement with hydrogenfinement (Steciuk et al. 2019b) toRSg(max) (crs1 and crs2)
0.6
the impossibility of solving and or
No. of reflections (obs/all)7089/38210
refining the structure from 3D ED
0.1523/0.1457
R, wR (obs)data (Zhao et al. 2017; Krysiak
350/196
N parameters/N struct. parameters
et al. 2018). In the latter cases, a
Crystal thickness (crs1, crs 2)476(8) Å and 322(3) Åquantitative analysis of the disorder is necessary to fully underindependent (Palatinus et al. 2015a, b). The data comstand the structure and the related properties (Brázda etpleteness reached 91% for a sinθ/λ = 0.7 Å–1 resolution
al. 2016; Neagu and Tai 2017; Zhao et al. 2017; Krysiak
shell after combining two data sets (Tab. 3). The structure
et al. 2018; Mugnaioli and Gorelik 2019).
was solved with Superflip (Palatinus and Chapuis 2007)
For 3D ED data collected on krupičkaite crystals,
and refined in Jana2006 (Petříček et al. 2014).
the R-values from the dynamical refinement are significantly lower than the kinematical ones and still reachreasonable values with R(obs) = 0.1523 and wR(obs) =6.3. Structure solution and refinement
0.1457 for 7089 unique observed reflections (Tab. 3).
Moreover, the dynamical refinement was more efficient
A complete structure solution was obtained with thein revealing hydrogen positions, despite some wereSuperflip program, and only the atomic types were adalready visible using the kinematical approximation
justed according to the relevant cation-oxygen distances.
(Steciuk et al. 2021). For these reasons, the structural
Surprisingly and considering the limited data quality, thedescription is based on the results of the dynamical reelectrostatic potential map presents very well-defined
finement that is considered, in this case, slightly more
peaks corresponding to the copper-arsenate layer. The
accurate than the kinematical one in terms of positional
cationic sites possessing cation-oxygen distances ofparameters. The low data resolution and the disorder
about 1.7 and 2 Å are attributed to arsenate and copper
did not allow the refinement of the atomic displacement
polyhedra, respectively.
parameters with the dynamical refinement. They were
For the refinement of krupičkaite structure against
set to the value obtained from the kinematical refine3D ED data, neither the kinematical refinement nor thement where only two values were refined: one uniquedynamical refinement is able to account for the diffuse
value for As and Cu atoms and one for all O atoms.
scattering visible along the stacking direction, and more
Moreover, to ensure the coordination polyhedra's stagenerally, inelastic scattering is not modeled (see secbility with reasonable cation-oxygen distances, restrictions in Fig. 3b) (Latychevskaia and Abrahams 2019).
Tab. 3 Summary of data collection conditions and refinement parameters for krupičkaite

42

Krupičkaite, a new copper arsenate from Jáchymov

Fig. 3 Reciprocal–space reconstruction: a) Projected within one unit cell; b) sections of the reciprocal space from PEDT data.

tions were applied on As–O, Cu–O and O–O distances.
The difference potential map allows the determinationof 14 hydrogen positions of the 18 expected despite avery noisy map. The last ones (labelled H1O1, H1O6,
H2O10, and H2O17) were deduced by geometry in order to stabilize them with a strong hydrogen bond as it
has been observed in geminite (Cooper and Hawthorne
1995; Prencipe et al. 1996). While the apparent O–H
distance is still an open question for electron diffraction
data (Clabbers et al. 2019), our data are not suitable
to test it and O–H distances were set to 0.98 Å with
the isotropic displacement parameters of the hydrogenatoms set as riding with an extension factor of 1.2 (Palatinus et al. 2017).

From the refinement, the hydrogen positions of theinter-channel water molecules are not visible in the difference potential map because the corresponding oxygensites are all partially occupied and most likely disordered.
The refined water content is 2.216 for Z = 4. This value
is probably a rough estimation since the atomic displacement parameters could not be refined. However, theexperience shows that in the case of a disordered site,
the refined occupancy is usually overestimated. Thus,
the formula of krupičkaite for Z = 4 is probably close toCu6(H2O)6[AsO3(OH)]6(H2O)2. It means that from our 3D
ED data collected under the TEM vacuum, only half of
the H2O sites intra-channel are occupied. Even though
the cryo plunging method was used, we cannot exclude
43

Gwladys Steciuk, Jiří Sejkora, Jiří Čejka, Jakub Plášil, Jan Hloušek

Fig. 4 a) Cation coordination polyhedra found in krupičkaite. b) Topology of the copper–arsenate layer. c) [001] projections of the structure
showing the stacking sequence of krupičkaite Cu6[AsO3(OH)]6·8H2O. d) Topology and stacking in geminite Cu(AsO OH)·H O (after Cooper and3
2
Hawthorne 1995).

an influence of the TEM vacuum on the apparent amountof water. The CIF file, also containing a block with thereflections, is deposited at the Journal’s webpage www.
jgeosci.org.

7. Crystal structure

7.1. Cation coordination and connectivity
The structure of krupičkaite possesses six Cu, six As,
thirty-four O (four of them belong to the water molecules
not-bonded directly to any metal cation), and eighteen H
sites when the hydrogen sites of the water in the channel
is not considered (14 have been directly revealed by thecurrent study) (Tab. 4). The copper sites were considered
to be only occupied by Cu2+, despite the fact that elevatedcontents of Ni and Co have been detected in the WDS
data. Due to similar atomic-scattering amplitude for electrons for Cu, Ni and Co, the refinement from PEDT dataof their respective occupancies was not possible. Hence,
all positions are treated in the refinements as fully occupied by Cu. In terms of coordination polyhedral, Cu2+ occupies both distorted square pyramids [4+1], and distorted
octahedra [4+2], while Cu1 site is in [4+2] coordination
with four O2– and two (H2O) groups. Cu2 and Cu6 sites
are also in [4+2] coordination but surrounded by five O2–
44

and only one (H2O) group. The Cu4 site is the only coppersite in octahedral coordination that is not bonded to any
water molecule because each of its vertices is connectedto the vertex of an As-tetrahedra. The Cu3 and Cu5 sites
are in [4+1] coordination with four O2– and one (H2O)
group. The coordination polyhedra around Cu are all distorted due to the Jahn–Teller effect (Burns and Hawthorne1995), inducing a wide range of Cu–O distances ranging
from 1.769(11) to 2.376(5) Å (Tab. 5 and Fig. 4a). All As
sites are in tetrahedral coordination and are occupied bypentavalent As ions. The average As–O distance of 1.68
Å was restricted during the refinement to stay within therange most-frequently exhibited by AsO4 tetrahedra. In thesame way, as for geminite, all As-groups are protonated,exhibiting three oxygen anions and one OH group forwhich the As–OH distance tends to be the longest As–O
distance in each of the tetrahedra (Tab. 5).
As shown in Figs 4b and c, krupičkaite possesses
an original topology with the copper-arsenate layer
forming a wave shape along the a-axis, that is characteristic of this mineral. Within one layer, the structureof krupičkaite is built upon infinite chains of CuΦ 5 andCuΦ6-polyhedra sharing edges to form infinite layers
parallel to (010) and linked together by As-tetrahedra toform infinite sheets. There are two symmetrically distinct
chains within one layer: one with only 6-coordinatedCu and another with a mixture of 5- and 6-coordinatedKrupičkaite, a new copper arsenate from Jáchymov

Tab. 4 Atom positions and displacement parameters (Å2) and bond–valence sums (BV, in valence–units) for krupičkaite as obtained from dynamicalrefinement
atom
x/a
y/b
z/c
Occ
BV#
Uiso*
As1
0.23482(13)0.8246(3)0.4930(2)15.03(4)0.0078(5)As20.60343(14)0.8189(3)0.4325(2)1
5.15(5)0.0078(5)As30.01903(14)0.7152(3)0.3008(2)1
5.30(5)0.0078(5)As40.32106(14)0.7841(2)0.1261(2)1
5.22(5)0.0078(5)As50.34173(14)0.6283(2)0.6385(2)1
5.31(5)0.0078(5)As60.49637(14)0.6214(2)0.2899(2)1
5.18(4)0.0078(5)Cu10.42094(19)0.6619(3)0.9650(3)1
1.94(2)0.0078(5)Cu2
0.61934(16)0.6851(3)0.6260(2)12.01(2)0.0078(5)Cu30.27092(15)0.7633(3)0.8018(2)12.18 (2)0.0078(5)Cu4
0.41916(17)0.7510(2)0.4643(3)1
2.23(2)0.0078(5)Cu50.56273(15)0.7662(3)0.1271(2)1
2.19(2)0.0078(5)Cu6
0.21644(16)0.6875(3)0.2970(2)12.02(2)0.0078(5)O10.6543(4)0.9058(4)0.4404(6)1
2.15(4)0.0142(7)O2
0.3386(4)0.5798(4)0.9895(7)12.29(5)0.0142(7)O30.5930(4)0.8605(5)0.0968(6)1
2.46(5)0.0142(7)O40.1821(4)0.7899(4)0.3448(5)12.00(2)0.0142(7)O50.1036(4)0.6525(5)0.3425(6)1
1.87(3)0.0142(7)O6
0.1929(4)0.9162(3)0.4854(7)1
2.09(4)0.0142(7)O70.2535(3)0.5676(4)0.6307(6)12.22(6)0.0142(7)O80.4963(4)0.6706(5)0.1543(4)1
2.18(3)0.0142(7)O90.5965(3)0.5747(3)0.6336(6)1
2.14(6)0.0142(7)O100.2421(4)0.5842(4)0.2437(6)12.25(5)0.0142(7)O110.6540(4)0.7878(5)0.5837(4)12.10(2)0.0142(7)O120.3285(3)0.6801(4)0.4989(5)1
1.92(2)0.0142(7)O130.0061(4)0.7539(4)0.4395(3)12.30(2)0.0142(7)O140.5057(4)0.6795(4)0.4242(5)1
1.86(2)0.0142(7)O150.5957(3)0.5714(3)0.3256(6)1
2.10(2)0.0142(7)O16–0.0750(4)0.6601(6)0.2673(5)1
2.18(4)0.0142(7)O170.5081(4)0.5656(3)0.9308(7)1
1.97(4)0.0142(7)O18
0.4154(3)0.5581(3)0.2433(6)1
1.80(3)0.0142(7)O190.2049(4)0.7824(4)0.6227(3)1
1.97(2)0.0142(7)O20
0.2597(3)0.8699(4)0.8498(5)1
2.17(5)0.0142(7)O210.6366(4)0.7710(6)0.3106(4)1
1.98(3)0.0142(7)O220.3458(2)0.8364(4)0.5051(5)1
1.83(2)0.0142(7)O23
0.4324(3)0.5751(3)0.6649(6)1
1.84(2)0.0142(7)O240.2411(3)0.8484(3)0.1059(5)1
1.83(2)0.0142(7)O25
0.4173(4)0.8390(5)0.1547(5)12.06(4)0.0142(7)O26
0.3528(3)0.6873(3)0.7662(5)1
2.18(3)0.0142(7)O27
0.4922(2)0.8233(9)0.4162(6)1
2.07(3)0.0142(7)O28
0.0120(4)0.7765(5)0.1738(6)1
1.93(3)0.0142(7)O29
0.3297(3)0.7219(5)0.2526(5)1
1.87(3)0.0142(7)O30
0.3179(4)0.7361(4)0.9859(4)12.15(2)0.0142(7)Ow1
0.0966(8)0.4688(7)0.0558(12)0.79(2)0.04(3)0.05(1)
Ow2
0.7994(11)0.5310(9)0.1887(16)0.56(2)0.30(1)0.05(1)
Ow3
0.5141(11)0.9703(8)0.223(3)0.33(2)0.03(2)0.05(1)
Ow4
0.3202(7)0.9860(4)0.0935(7)0.53(2)0.50(2)0.05(1)H1o1
0.1921(17)0.594(4)0.0319(10)11.01(3)0.01704
H1o2
0.2792(6)0.598(2)0.942(2)1
1.01(3)0.01704
H2o2
0.3376(10)0.573(4)0.0838(12)11.05(3)0.01704
H1o3
0.6027(17)0.849(2)0.0080(10)11.08(4)0.01704
H2o3
0.6555(9)0.8725(16)0.1413(18)11.01(3)0.01704
H1o6
0.1661(18)0.9654(6)0.500(4)10.98(4)0.01704
H1o7
0.232(2)0.5334(17)0.555(3)10.95(6)0.01704
H1o9
0.6416(5)0.5383(12)0.680(3)10.95(4)0.01704
H2o9
0.5438(7)0.5529(10)0.659(3)1
1.06(4)0.01704
H1o10
0.2064(11)0.5427(10)0.2688(13)10.95(4)0.01704
H2o10
0.3037(9)0.5663(15)0.248(4)1
1.04(4)0.01704
H1o15
0.6103(9)0.5171(3)0.334(4)1
1.05(2)0.01704
H1o16–0.0909(18)0.670(3)0.1706(9)1
1.05(3)0.01704
H1o17
0.5710(6)0.566(4)0.923(3)1
1.01(3)0.01704
H2o17
0.4688(9)0.5513(15)0.8445(8)11.02(2)0.01704
H1o20
0.2328(4)0.9199(5)0.857(3)10.99(2)0.01704
H2o20
0.3009(11)0.8736(17)0.7898(19)11.01(4)0.01704
H1o25
0.445(2)0.8196(11)0.2444(9)11.05(3)0.01704* Isotropic displacement parameters are from the kinematical refinement. # – bond-valence parameters are taken from Gagné and Hawthorne (2015)

45

Gwladys Steciuk, Jiří Sejkora, Jiří Čejka, Jakub Plášil, Jan Hloušek

Tab. 5 Selected interatomic distances (in Å) and angles (°) in the structure of krupičkaite
O–H (OH)O1–H1O1
O6–H1O6
O7–H1O7
O15–H1O15
O16–H1O16
O25–H1O25
O–H (H2O)

0.982(14)0.983(19)0.98(3)0.980(9)0.981(13)0.980(14)O2–H1O2
0.980(17)O2–H2O2
0.981(17)O3–H1O3
0.98(2)O3–H2O3
0.980(15)O9–H1O9
0.98(2)O9–H2O9
0.98(2)
O10–H1O10
0.98(2)
O10–H2O10
0.983(17)O17–H1O17
0.981(15)O17–H2O17
0.980(12)O20–H1O20
0.980(11)O20–H2O20
0.98(2)angle H1Oi–Oi–H2Oi [°]
O2
O3
O9
O10
O17
O20

108(2)98(2)98(2)
109(2)
109(2)
109(2)

Cu–O
Cu1–O2
Cu1–O8
Cu1–O13
Cu1–O17
Cu1–O26
Cu1–O30
Cu2–O4
Cu2–O9
Cu2–O11
Cu2–O14
Cu2–O24
Cu2–O28
Cu3–O19
Cu3–O20
Cu3–O21
Cu3–O26
Cu3–O30
Cu4–O12
Cu4–O14
Cu4–O22
Cu4–O27
Cu4–O28
Cu4–O29
Cu5–O3
Cu5–O8
Cu5–O13
Cu5–O19
Cu5–O21
Cu6–O4
Cu6–O5
Cu6–O10
Cu6–O11
Cu6–O12
Cu6–O29

1.968(8)2.023(5)2.027(8)2.230(7)2.113(5)2.093(7)2.273(5)1.977(8)1.960(9)2.376(5)2.004(5)1.937(7)1.911(4)1.957(8)2.157(7)1.922(7)1.921(5)1.955(7)1.936(7)1.975(7)1.833(12)2.336(6)2.341(5)1.769(11)2.015(9)1.953(4)2.342(7)1.961(5)1.969(8)1.984(7)1.963(8)2.220(5)2.366(5)1.981(6)As–O
As1–O4
As1–O6
As1–O19
As1–O22
As2–O1As2–O11
As2–O21
As2–O27
As3–O5
As3–O13
As3–O16
As3–O28
As4–O24
As4–O25
As4–O29
As4–O30
As5–O7
As5–O12
As5–O23
As5–O26
As6–O8
As6–O14
As6–O15
As6–O18

Cu atoms that are linked by vertices with AsO4 tetrahedra along [–101]. The As-tetrahedra ensure the link
between the Cu chain within one layer by three of their
vertices, while the last one is staggered towards the interlayer and corresponds to the acid group. This groupis further involved in hydrogen bonding and, thus, thelayers' cohesion following the stacking direction. The
layered structure of krupičkaite presents the alternationof [Cu(AsO3(OH))(H2O)]0 sheets and an interlayer ofmolecular H2O stacked along b (Figs 4c and 5). The

1.664(6)1.729(7)1.679(6)1.680(4)1.708(8)1.659(6)1.683(8)1.667(4)1.675(7)1.632(5)1.699(8)1.676(7)1.640(6)1.724(7)1.681(7)1.661(5)1.705(6)1.672(6)1.639(5)1.651(6)1.641(7)1.697(6)1.716(5)1.649(6)distance between two copperarsenate layers varies from 2.58
Å (like in geminite) to 5.92
Å, which results in channels
running along c and occupied
by molecular water (Figs 4b
and 5).

7.2. Structural formula

The bond valence analysis, aswell as the refinement of 3D ED
data, gives an average composition of Cu6(H2O)6[AsO3(OH)]6
with about 2.2 additional H2O
in the channel (Tab. 5). This
result is consistent with the formula obtained after the chemical analyses of krupičkaite byelectron microprobe. The latest analysis allowed the detection of a non-negligible amountof Co, Ni and Zn sharing thecopper sites. In theory, theamount of water intra-channel
can range from 0 to 4 when all
water oxygen sites are either
empty or fully occupied, leading to theoretical compositions
from Cu6[AsO3(OH)]6·6H2O toCu 6 [AsO 3 (OH)] 6 ·10H 2 O. On
average, krupičkaite possesses 8H2O (with 2 intra-channel
H 2O). The likely local variation of the water content in
the channel within one crystalof krupičkaite may result in a stretching/shrinking of
the channel’s height along b. The stacking disorder in
krupičkaite is then easily explained by the possible cleavage between the two kinds of sheets linked by stronghydrogen bonds and the likely flexibility of the intrachannel H2O content and the H2O connectivity. In thisway, krupičkaite tend to behave like a 2D structure. The
vast diversity of O–H···H bonds present in this mineralis supported by the Raman spectroscopy.

Tab. 6 Overview of related layered cooper-arsenate minerals
MineralComposition
As/Cu (overall) As/Cu (As–Cu layer)
As–Cu (layer)
Interlayer
Krupičkaite Cu6[AsO3(OH)]6·8H2O
1
1
Chain 1: CuΦ5 and CuΦ6; Chain 2: CuΦ6
H 2O
GeminiteCu(AsO3OH)·H2O
11
Layer 1: CuΦ5 and CuΦ6; Layer2: CuΦ6
H 2O
Slavkovite Cu13(AsO4)6(AsO3OH)4·23H2O
1.3
1.1
CuΦ5 and CuΦ6
CuΦ4 and H2O
Ondrušite
CaCu4(AsO4)2(AsO3OH)2·10H2O
1
1
CuΦ5 and CuΦ6
CaΦ6 and H2O
Lindackerite CuCu4(AsO4)2(AsO3OH)2·9H2O
1.25
1CuΦ5 and CuΦ6
CuΦ6 and H2O
YvoniteCu[AsO3(OH)]·2H2O
1
1
CuΦ4
H 2O

46

Krupičkaite, a new copper arsenate from Jáchymov

Fig. 5 Schemes of the stacking for krupičkaite (left) and geminite. The dashed lines represent O–H···O bonds and the O–H as well as hydrogen–bonds.

7.3. Comparison with related minerals
Considering the composition, the cation coordination, as
well as the topology, the structure of krupičkaite is closely
related to geminite, Cu(AsO3OH)·H2O. At first sight andfrom the composition, one could consider krupičkaite to
be a hydrated geminite with an additional 2/3 H2O (Figs
4d and 5). However, a closer look at the topology of thetwo minerals reveals essential differences. In geminite, theCu chains are linked the same way as in krupičkaite, butthere are two different layers along the stacking direction
c instead of one in krupičkaite: one with all the copperin octahedral coordination and the other presenting bothoctahedral and square pyramidal coordinations (Fig. 4d).
Furthermore, the hydroxyl groups (acid groups) and theH2O linked to As and Cu emanate out of the layers towards the next copper-arsenate layer, stabilizing the entire
structure by hydrogen bonds (Fig. 5). In krupičkaite, thesame feature is observed when two Cu-As layers are 2.58
Å away, while in the channels, the hydrogen bonds occur between the hydroxyl or the water molecules of thecopper-arsenate layer and/or the surrounding water ofthe channel. The partial presence of water in the channel
implies that the copper-arsenate layers are not linked bystrong hydrogen bonds on all their surface, explaining
well the easy cleavage observed in krupičkaite.

More generally, krupičkaite is related to several otherlayered copper arsenate minerals initially found in the
Jáchymov ore district. Some of them possess the same, orclose, As/Cu ratio of the As-Cu layers such as slavkovite(Sejkora et al. 2010c), other minerals of the lindackerite
supergroup (Sejkora et al. 2011; Plášil et al. 2014a, b),or yvonite (Sarp and Černý 1998) among others (Tab. 6).
Interestingly, except for yvonite that is built from infinite layers of CuΦ4 linked with AsO4 tetrahedra, otherminerals present very characteristically collapsed copper
chains in the arsenate-copper sheets. In krupičkaite, only
one As-Cu layer is present but with two distinct chains,
whereas, in slavkovite and minerals of the lindackerite
supergroup, the main copper-arsenate layer is built uponchains with a mix of CuΦ5 and CuΦ6 polyhedra similarly
bonded through AsO4 tetrahedra. Slavkovite is anotherexample of a highly hydrated mineral with a very thickwater interlayer that seems to adopt a somewhat wavyarsenate copper sheet like in krupičkaite.
Acknowledgments. The manuscript benefited from thethorough reviews of two anonymous reviewers. This
research was financially supported by the project Czech
Science Foundation (project GACR 17–09161S) to
JP and JS and supported by Operational Programme
Research, Development and Education financed by47

Gwladys Steciuk, Jiří Sejkora, Jiří Čejka, Jakub Plášil, Jan Hloušek

European Structural and Investment Funds and the Czech
Ministry of Education, Youth and Sports (Project No.
SOLID21 CZ.02.1.01/0.0/0.0/16_019/0000760). We also
acknowledge the support of the LNSM Infrastructure
supported by MEYS CR (LM2018110).
Electronic supplementary material. Supplementary material, consisting of the crystallographic information filefor krupičkaite is available online at the Journal web site(http://dx.doi.org/10.3190/jgeosci.318).

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